Multi-scale porous Ti6Al4V scaffolds with enhanced strength and biocompatibility formed via dynamic freeze-casting coupled with micro-arc oxidation

doi:10.1016/j.matlet.2016.08.075

Materials Letters

Volume 185, 15 December 2016, Pages 21-24

https://doi.org/10.1016/j.matlet.2016.08.075 Get rights and content

Highlights

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The multiscale porous Ti6Al4V scaffold was produced by coupling DFC with MAO.
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The addition of EtOH in MAO solution permitted coating on the interior pore walls.
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The mechanical properties of porous Ti6Al4V were controlled by adjusting porosity.
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The MAO coating enhanced biocompatibility.

Abstract

Titanium implants with sufficient mechanical properties and biocompatibility have been in demand for rapid healing and successful surgery. Herein, porous Ti6Al4V scaffolds with multi-scale porosity were obtained by coupling dynamic freeze-casting with micro-arc oxidation (MAO). The fabricated scaffolds exhibited tailored pore sizes and interconnected pores. Compressive strength and elastic modulus were controlled by adjusting the porosity of the scaffolds. MAO was successfully conducted on the porous Ti6Al4V scaffolds by inhibiting gaseous emission from the electrolysis of water with the addition of ethanol to the MAO solution. Moreover, the biological response of preosteoblasts on the multi-scale porous Ti6Al4V scaffolds was enhanced owing to their porous topography and modified chemical composition.

Introduction

Porous titanium (Ti) has received considerable attention as biomedical scaffolds such as orthopedic and dental implants with load-bearing capacities [1], [2]. It provides a suitable environment for bone repair and reduces the mismatch in elastic modulus between bone and implants [3], [4]. A porous structure leads to high conductivity; however, mechanical properties of porous Ti tend to trade off [1], [5]. With sufficient mechanical properties, porous Ti alloys have emerged as a promising solution [6]. However, additional surface treatments that can improve surface roughness and osteoinductivity of these materials to improve their performances in physiological environments are still required [4].

Micro-arc oxidation (MAO) can potentially solve the abovementioned problem as it can produce thick and stable micro-/nanoporous coating layers [7], [8]. Moreover, Ca and P ions can be incorporated in the MAO electrolyte to generate a TiO₂-based coating layer that can improve osteoblast cell responses on the surface and potentially block the release of toxic ions [9]. Consequently, Ti alloys with multi-scale macro-/microporous structures and improved biocompatibility can be readily fabricated via MAO. However, the coating process creates gaseous emissions due to the electrolysis of water during MAO; these gases can get trapped in the narrow and non-interconnected pores of the scaffold, hindering the formation of a uniform TiO₂ coating layer within the pores [10], [11].

Therefore, in this study, we demonstrate the fabrication of multi-scale porous Ti6Al4V scaffolds by coupling dynamic freeze-casting (DFC) with MAO to obtain good mechanical properties and biocompatibility. DFC is a noteworthy method used to fabricate porous metal with controllable pore size, interconnected, and mechanical properties. In this study, Ti6Al4V powder/camphene slurries with various Ti6Al4V contents (15, 20, and 25 vol%) were cast in rotation to produce different final porosities and pore sizes [12]. An electrolyte solution containing ethanol and bioactive ions were used for MAO to reduce the gaseous emission on the electrode and enhance the biocompatibility at the scaffold surface, respectively. The fabricated porous Ti6Al4V scaffolds were characterized in terms of porous structure, and the mechanical and biological properties were evaluated.

Section snippets

Experimental procedure

Ti6Al4V powder and camphene were used as the starting materials. Ti6Al4V/camphene slurries with various Ti6Al4V contents (15, 20, and 25 vol%) were prepared by ball milling at 60 °C. The warmed slurries were poured into a mold and rotated at 30 rpm at 44 °C. After demolding, the frozen bodies were freeze-dried to remove the camphene. Subsequently, the samples were sintered at 1250 °C for 2 h in vacuum. Porous Ti samples fabricated by the same procedure were also fabricated as controls. An electrolyte

Results and discussion

The porosities estimated by micro-CT were 71%, 61%, and 51% for the scaffolds with initial Ti6Al4V contents of 15, 20, and 25 vol%, respectively, while the corresponding pore sizes were 426, 312, and 311 µm, respectively. These results demonstrated that the pore properties can be easily tailored by manipulating the initial amount of Ti6Al4V. A scaffold with low Ti6Al4V content can be used to produce a porous structure with relatively large pores and high porosity, which can then be subjected to

Conclusions

Porous Ti6Al4V scaffolds with multi-scale porosity were fabricated by DFC integrated with MAO. Compressive strength and elastic modulus were controlled by adjusting the porosity of the scaffolds. The porous Ti6Al4V scaffolds were successfully treated by MAO by providing sufficient large and interconnected pores using DFC and inhibiting gaseous emissions due to the electrolysis of water by adding ethanol to the MAO solution. Moreover, in the in vitro cell attachment and proliferation tests, the

Acknowledgments

This research was supported by Basic Science Research Program (No. 2015R1D1A1A01057311) through the National Research Foundation of Korea and Technology Innovation Program (10037915 , WPM Biomedical Materials–Implant Materials) funded by the Ministry of Education and the Ministry of Trade, Industry & Energy.

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Multi-scale porous Ti6Al4V scaffolds with enhanced strength and biocompatibility formed via dynamic freeze-casting coupled with micro-arc oxidation

Highlights

Abstract

Introduction

Section snippets

Experimental procedure

Results and discussion

Conclusions

Acknowledgments

Biomaterials

Biomaterials

Mater. Des.

Surf. Coat. Technol.

Surf. Coat. Technol.

Acta Biomater.

Ceram. Int.

Mater. Sci. Eng. C